Light weight wave guide construction



E. LOVICK, JR

LIGHT WEIGHT WAVE GUIDE CONSTRUCTION Feb. 26, 1957 Filed Jan. 26, 1955 INVENTOR. EDWARD LOVICK JR.

gent LIGHT WEIGHT WAVE GUIDE CONSTRUCTION Edward Lovick, Jr., Van Nuys, Califi, assignor to Lockheed Aircraft Corporation, Burbank, Calif., a corporation of California Application .lanuary 26, 1955, Serial No. 484,115 6 Claims. (Cl. 33395) This invention relates, in general, to waveguides, and more particularly to a light-weight waveguide construction which is specially suited for uses where it is necessary to pressurize the waveguide cavity for improving the waveguide energy transmitting characteristics.

Pressurizing the waveguide in an energy transmission line permits controlling the moisture level inside the guide and allows the transmission of energy at higher power levels than would be possible with the same waveguide at atmospheric pressure. This effect of moisture and pressure on the operative efliciency of a waveguide makes it frequently necessary, particularly in airborneelectronic installations, to provide means for pressurizing the Waveguide.

In order to propagate electromagnetic energy in a mode which is compatible with present day electronic equipment it is essential that the waveguide be generally rectangular in cross-sectional shape. When such a waveguide shape is subjected to internal pressure there is obviously a strong tendency for the walls of the guide to bulge outwardly, thus requiring a rather rugged structure to prevent such deformation in pressurized wave guide applications. The conventional pressurized waveguide employs thick brass, aluminum or other metallic tubing, sometimes in the form of corrugated tubing, covered with a thick plastic jacket. This construction is obviously quite heavy and, therefore, in airborne wave guide applications, pressurized waveguides have been restricted to use where it is absolutely essential even though more extensive use would greatly increase the efiiciency of the associated electronic equipment.

An object of this invention is to provide a light-weight waveguide which will maintain the required rectangular cross-sectional shape under the application of high internal pressures for propagating electromagnetic energy in a mode which is compatible with present day electronic equipment.

Another object of this invention is to provide a lightweight waveguide construction which may utilize fabric as the basic structural element in combination with a thin conductive coating for effecting the propagation of energy. With this construction, the waveguide may be made collapsible to facilitate its storage and delivery and expandable to a stiff and properly shaped structure for the transmission of energy by simply applying an internal pressure greater than the pressure existing externally of the waveguide.

Still another object of this invention is to provide a light-weight pressurized waveguide construction which may be readily and economically fabricated with a mini mum use of critical materials.

Further and other objects will become apparent from a reading of the following description, especially when considered in combination with the accompanying drawing wherein like numerals refer to like parts.

In the drawing:

Figure l is a fragmentary perspective View of a section of the waveguide of this invention;

2,783,440 Patented Feb. 26, 1957 Figure 2 is a cross-sectional view of the waveguide;

Figure 3 is a view schematically showing a typical installation of the waveguide; and

Figures 4 and 5 are cross-sectional views of modified forms of the waveguide shown in Figures 1 and 2.

Referring to Figure l, the waveguide includes an outer tubular member 1 and an inner tubular member 2 concentrically arranged within the outer member. Outer member 1 may be made of any material having sufficient strength to withstand the maximum internal waveguide pressure but preferably is constructed of a flexible woven fabric such as cloth which is sealed by impregnating the same with rubber or synthetic resin. Inner tubular member 2 may also be of any suitable material or composition of materials but preferably it is a woven fabric such as cloth lined with a conductive coating 8. As best shown in Figure 2, inner tubular member 2 is suitably secured to outer member 1 at four spaced seams 3, 4, 5 and 6, such as by sewing the fabric at these points wherein the inner tubular member will be pulled into a generally rectangular cross-sectional shape of the desired dimensions for the propagation of electromagnetic energy in the desired mode when outer member 1 is gen: erally circular in cross section.

When cloth fabric 7 is employed in making inner tubular member 2, it is essential that a conductive coating 8 be secured to the inner wall thereof to provide for the propagation of energy, as in a conventional all metal waveguide. This conductive coating 8 may be applied to the fabric 7 by simply spraying orbrushing the same with metalized paint or by other suitable means. It should be understood, however, that the inner tubular member 2 may be made of thin metal foil, woven metal screen material, perforated sheet metal, or any other conducting system which will propagate electromagnetic energy. The strength of the inner tubular member is actually of rather minor significance since itsv rectangular cross-sectional shapeis obtained by maintaining a generally circular cross-sectional shape for outer tubular member 1.

In order to relieve inner tubular member 2 of stresses due to pressurizing the waveguide to obtain improved electrical benefits as well as to provide a still waveguide structure, a plurality of perforations 9 are formedin the inner tubular member, allowing fluid communication from one side thereof to the other. Thus, as the waveguide is pressurized, the pressure ditlerential between the inside and outside surfaces of the inner tubular member remains substantially zero, allowing the use of thin, lightweight materials. Only as many perforations as are necessary to provide a uniform presure distribution inside the waveguide should be formed in the inner tubular member so as not to materially alter the electrical characteristics of the waveguide as compared with one without perforations. It is also important, to prevent the leakage of energy, that the size of perforations 9 be small, normally not larger in diameter than one-tenth of a wave length of the energy flowing in the waveguide.

A typical installation using the waveguide shown in Figures 1 and 2 is shown in Figure 3 wherein a signal generator 10 produces energy to be transmitted through a suitable antenna 11 at a location remote from the signal generator. A waveguide transmission line 12 is coupled with signal generator 10 and antenna 11 to provide a confined path for the efficient propagation of energy to the antenna. The pressurized portion 13 of transmission line 12 is coupled at either end 14 and 15 to short segments of standard waveguide coupling elements 16 and 17. A radially outwardly directed flange 18 on each waveguide coupler 16 and 17 engages a radially outwardly directed flange 19 formed on outer tubular member 1 of the light-weight pressurized waveguide segment sucha's bolts 21, securely fasten Waveguide segment 13 to antenna 11 and to signal generator through the coupling elements. A pressure sealing window 22 of mica, glass, quartz, or'the like, is insertedin'the transmission line at either end of the pressurized waveguide segment 13 to provide a pressure'tight seal which will allow maintaining the lightweight waveguide segment under the desired internal pressure load and yet will not noticeably obstruct the flow of electromagnetic energy through the Waveguide transmission line 12.

Waveguide segment 13 may be pressurized by any suitable means, such as by employing a pressure bottle .23 which communicates with the waveguide segment through'line 24, or, if leakage is sufliciently slow, the waveguide maybe initially pressurized and then sealed, providing a completely self-contained unit.

While an energy transmitting system is shown in Figure 3, it is merely to illustrate a use of the light-weight waveguide construction, it being obvious that the same may be used to advantage in practically all waveguide applications.

In assembling the light-weight waveguide using a flexible material for outer tubular member 1, it is best to complete fabrication of the inner tubular member by metalizing the inner wall and forming perforations therein before fastening the inner and outer walls together. After completing the fabrication of inner tubular member 2, the outer tubular member 1 is sewn, or otherwise'suitably bonded, to the inner members at seams 3, 4, 5 and 6 and then a fluid-tight seam 25 joining the free ends of the fabric forming the outer tubular member is made by bonding or sewing the overlapped ends together.

In fabricating the waveguide there is a wide selection of materials available since there are only three basic design requirements in that the outer tubular member must have suificient strength to Withstand the internal pressures and it should be substantially fiuid tight while the inner tubular member need only have the inner wall thereof conductive for propagating energy. While the shape of the inner tubular member is important for ropagating energy in a suitable mode, this is primarily accomplished in the construction of the waveguide rather than by the selection of high strength, stifl materials. The location of seams 3, t, 5 and 6 to efiect a rectangular cross-sectional shape for the inner tubular member when the outer tubular member is generally circular in cross section provides a highly satisfactory waveguide design from the standpoint of both structural and electrical efliciency.

By the selection of flexible materials for both the inner and outer tubular members of the waveguide, handling problems are greatly simplified since the waveguide may be flattened and rolled for storage and shipping purposes. When a specific use for such a waveguide exists the desired length of waveguide may be cut from the roll. By simply sealing the ends of the waveguide as described in connection with Figure 3 and applying fluid pressure in ternally of the waveguide segment, it will be caused to expand into the shape illustrated by Figures 1 and 2 w erein the inner tubular member is generally rectangu- Jar in cross section. Of course it is not essential to the teachings of this invention that either the inner tubular member or the outer tubular member be made of flexible material. The same benefits with respect to structural and electrical efficiency will be obtained using a rigid contraction; the only diflerence being in the method of storing and handling the waveguide since with a rigid structure it would not be possible to store quantities thereof in rolls, as previously described.

A modification of the waveguide of Figures 1 and 2 is shown in Figure 4 wherein an outer tubular pressure resisting member 26 encases an inner tubular member 27 forming a plurality of separate perforated waveguides contiguously arranged for independently propagating energy therethrough. The construction and operation of 4 this modified version is the same as described above in connection with Figures 1, 2 and 3.

A second modification of the waveguide construction is shown in Figure 5 wherein the narrow wall 28 of inner tubular member 29 also forms a part of outer tubular member 30. While the inner tubular member will thus only approximate the desiredrectangular cross-sectional shape, it may be a preferable. construction for some pressu'riz'e'd waveguide applications because of its simplicity and adaptability to morerapid pressure changes. I

It is to be understood that certain alterations, modifications and substitutions may be made to the instant disclosure withoutdeparting from the spirit and scope of this invention as defined by the appended claims.

I claim:

I. An internal pressure resisting, light-weight waveguide comprising, .a flexible fluid-tight outer tubular member, a flexible tubular inner member concentrically arranged Within said fluid-tight cuter tubular member, said inner member connecting with said outer member at four spaced seams whereby said inner member provides a cavity generally rectangular in cross section when said outer member is generally circular in cross section, said inner member having a plurality of perforations formed therein whereby a substantially uniform pressure exists inside the waveguide at all times, and a metal coating secured to the inner Walls of the inner tubular member for propagating electrical energy therethrough.

2. An internal pressure resisting, light-weight waveguide comprising, a flexible outer tubular member, a flexible inner tubular member carried Within the outer member, said inner member connecting with said outer member at four spaced seams whereby pressurization of the waveguide causing the outer tubular member to become generally circular in cross section causes the inner tubular member to become generally rectangular in cross section, a conductive coating secured to the inner walls of said inner tubular member for propagating electromagnetic energy therethrough, and perforations formed in said inner tubular member for maintaining asubstantially equal and uniform pressure inside both the inner and outer members of the waveguide whereby the rectangular cross-sectional shape of the inner member may be maintained over a wide range of internal pressures for propagating the energy in a desired mode.

3. A light-weight pressurized waveguide through which electromagnetic energy may be propagated comprising, a

flexible outer tubular inember, a flexible inner tubular member generally concentrically arranged relative to the outer member, said inner member connecting with said outer member at a plurality of spaced seams to fonn walled polygonal cross sectional shape when the outer member is generally circular in cross section, the inner walls of said inner member being conductive for propagating electromagnetic energy in the desired mode, and means pressuriz'ing the inside of said waveguide for structurally stabilizing the same and increasing its electrical efliciency.

4. A waveguide through which electromagnetic energy may be propagated comprising, a flexible outertubular member, a flexible inner tubular member of conductive material generally concentrically arranged relative to the outer member, means connecting the inner member with the outer member at four spaced seams arranged generally parallel to each other whereby said inner member is urged to maintain a generally rectangular cross-sectional shape when said outer member is generally circular in cross section, means pressurizing the inside of said waveguide for increasing both the structural stability and electrical efficiency thereof, said inner member having a plurality of perforations formed therein for maintaining a uniform pressure distribution within the waveguide.

5. A light-weight waveguide for propogating electromagnetic energy comprising, a flexible outer tubular member generally circular in cross section for efliciently withstanding internal pressure, a plurality of flexible inner with each other and with the outer member at four spaced seams arranged generally parallel with each other whereby said inner members are maintained in a generally rectangular cross-sectional shape when said outer member is generally circular in cross section, and means pressurizing the inside of said waveguide, said inner members having a plurality of perforations formed therein for maintaining a substantially equal and uniform pressure inside both the inner and outer members of the .waveguide whereby the rectangular cross-sectional shape of the inner members may be maintained over a wide range of internal pressures for propagating energy therethrough in the desired mode.

6. An internal pressure resisting light-weight waveguide through which electromagnetic energy may be propagated comprising, a flexible tubular member generally circular in cross section for efiiciently withstanding internal pressure, and a flexible conductive inner tubular member generally concentrically arranged within the outer tubular member and secured to the outer member by at least four spaced seams to provide at least two generally flat Walls when the outer member is generally circular in crosssection for propagating energy through the waveguide in the desired mode, the generally flat walls having perforations formed therein for maintaining a substantially uniform pressure distribution Within the waveguide.

References Citedin the file of this patent UNITED STATES PATENTS 2,657,364 Carr Oct. 27, 1953 FOREIGN PATENTS 644,749 Great Britain Oct. 18, 1950 

